Plastic handles of various shapes and sizes are found on many household items. Such household items include toothbrushes, shaving razors, hairbrushes, pens, tools, kitchen appliances and kitchen utensils. These household items have a variety of functions, but in most cases, it is desirable for the user to grip the handle of these items firmly, so that it does not fall out of the user's hand. In other cases, such as with a knife or fork or a tool, it is desirable for the item to be gripped with even more firmness so that it can be leveraged.
Because the handles of these household items are normally made of a hard plastic, the simplest tasks can become problematic. As in the case of a toothbrush or shaving razor, the handle generally comes into contact with water. When the toothbrush or razor is wet, it is difficult to grip and may slip out of the user's hands. Other items such as tools or kitchen utensils can have handles that are difficult to hold onto or uncomfortable to grip because of the hardness of the plastic material. For persons suffering from arthritis, carpal tunnel syndrome or other hand injuries or infirmities, using these basic household objects can become more difficult or even impossible.
Most people would prefer to grip objects with a softer handle that is more soothing to the touch and easier to grip. Accordingly, a need exists for a soft grip handle that can be grasped firmly and comfortably, which requires minimum strength and dexterity to grip and maneuver, and that has a good balance of compression set and oil resistance properties.
U.S. Pat. No. 3,758,643 discloses blends of partially cured monoolefin rubber such as ethylene-propylene-diene rubber (EPDM) with a polyolefin resin where the rubber phase was cured with a peroxide curing agent. The compositions were useful as thermoplastic elastomers and contained a thermoplastic resin.
U.S. Pat. No. 4,104,210 discloses compositions of blends of vulcanized high diene rubbers with crystalline thermoplastic polyolefin resins. The diene rubbers include copolymers of diene with styrene, vinyl pyridine, acrylonitrile or methacrylonitrile. The compositions were of higher hardness and contained a thermoplastic polyolefin resin.
U.S. Pat. No. 4,130,535 discloses blends of polyolefin resins and completely cured monoolefin copolymer rubber such as EPDM.
U.S. Pat. No. 4,183,876 discloses thermoplastic compositions of crystalline thermoplastic polyolefin resins and cross-linked polyalkenamer rubber.
U.S. Pat. No. 4,202,801 discloses dynamically and partially cured blends of monoolefin copolymer rubbers such as ethylene-propylene copolymer rubbers or ethylene-propylene-diene terpolymer rubbers, polyolefin resin, and conjugated diene rubbers such as cis-1,4 polyisoprene or cis-polybutadiene or polychloroprene.
U.S. Pat. No. 4,203,884 discloses blends of polynorborene, plasticizer, and thermoplastic polyolefin resin.
U.S. Pat. No. 4,311,628 relates to blends of polypropylene and EPDM where EPDM was cured with phenolic resins for better oil resistance.
U.S. Pat. No. 4,271,049 discloses blends of crystalline polypropylene and cured rubbers including styrene-butadiene rubber up to 25 weight % styrene or alpha-methyl styrene and the rubber is cured with phenolic or urethane or sulfur donor curative. The preferred compositions were from 25–75 parts of polypropylene and about 75–25 parts of rubber.
U.S. Pat. No. 4,183,876 teaches blends of crosslinked polyalkenamer rubber and crystalline thermoplastic blends.
U.S. Pat. No. 4,340,684 is similar to U.S. Pat. No. 4,250,273 and further teaches partial curing of the rubber and narrows the claims for the melt flow rate of the formed blend. A thermoplastic resin was required for the preparation of the compositions.
U.S. Pat. No. 4,343,918 claims processes for making blends primarily disclosed in U.S. Pat. No. 4,250,273.
U.S. Pat. No. 4,594,390 discloses a process for preparation of thermoplastic elastomers of polypropylene and EPDM under conditions of high shear required for dynamic vulcanization of the EPDM. Here again, a polypropylene resin was required for the dynamic vulcanization of the crosslinkable elastomer.
U.S. Pat. No. 5,021,500 teaches TPO compositions prepared with a crystalline thermoplastic resin and a halobutyl rubber.
U.S. Pat. No. 5,051,478 provides a dynamically vulcanized composition comprising of a polyolefin resin, an elastomer, and an ethylene copolymer resin such as a copolymer of ethylene and vinyl acetate or an alkyl acrylate.
U.S. Pat. No. 5,248,729 suggests the process for making thermoplastic composition by heat treating a mixture of a thermoplastic resin with no olefinic unsaturated carbon-carbon bond, an elastomer from the group of SBS, SIS, 1,2-polybutadiene rubber, and EPDM rubber, with a crosslinking agent of dihydroaromatic compound.
U.S. Pat. No. 5,523,356 teaches blends obtained by dynamic vulcanization of polypropylene, polyisobutene, EPDM rubber, and polybutadiene.
U.S. Pat. No. 5,621,045 discloses thermoplastic vulcanizates from semi-crystalline polyolefins and blends of crosslinked rubbers with one rubber being C4 to C7 isomonoolefin based (isobutylene) and rubber being EPDM or rubbers derived from a conjugated diene.
U.S. Pat. No. 6,051,681 discloses process for preparation of thermoplastic elastomer with a rubber such as ethylene-alpha-olefin diene terpolymer (EPDM) and a thermoplastic resin, phenolic curative, a hydrotalcite and a HALS compound.
U.S. Pat. No. 6,207,761 discloses thermoplastic ionomer blend or alloy composition containing an ionomer, crosslinked rubber and polyolefin resins.
U.S. Pat. No. 4,250,273 suggests a thermoplastic elastomer composition comprising from about 10 to about 50 parts of a crystalline olefin polymer, from about 80 to about 15 parts by weight of a random styrene-butadiene rubber, and about 5 to about 55 parts by weight of a highly saturated elastomer.
U.S. Pat. No. 4,340,684 suggests a thermoplastic elastomer composition comprising from about 10 to about 50 parts of a crystalline olefin polymer, from about 80 to about 15 parts by weight of a random styrene-butadiene rubber, and about 5 to about 55 parts by weight of a highly saturated elastomer, where in the blend was partially cured so that a thermoplastic elastomer was formed which had a melt flow index of at least 1.0 when tested in accordance with ASTM D 1238 condition L at a load of 100 pounds. The authors suggest that when the melt flow rate of the formed blend was less than 1.0, thermosetting formulations were formed.
U.S. Pat. No. 4,343,918 claims the process for making a thermoplastic elastomer composition comprising from about 10 to about 50 parts of a crystalline olefin polymer, from about 80 to about 15 parts by weight of a random styrene-butadiene rubber, and about 5 to about 55 parts by weight of a highly saturated elastomer.
U.S. Pat. No. 4,803,244 teaches the process for preparation of a thermoplastic elastomer comprising mixing an elastomer containing carbon-carbon double blond, a saturated thermoplastic resin such as polyethylene, polypropylene, polystyrene, nylon 6, nylon 66, nylon 11, and nylon 12, and dynamically crosslinking the elastomer with a hydrosilation crosslinking system. The obtained thermoplastic compositions were of high hardness and the thermoplastic resin was essential for the preparation of the composition.
U.S. Pat. No. 4,927,882 claims a thermoplastic elastomer composition having a compression set less than about 30% and produced by dynamic vulcanization of SBR to form a dispersed phase of crosslinked SBR in a co-continuous matrix of SEBS and polypropylene. The compositions had specific use in the pharmaceutical applications.
U.S. Pat. No. 5,672,660 teaches an improvement in the process for the preparation of a thermoplastic elastomer composition comprising a blend of a thermoplastic olefin resin and an unsaturated rubber, wherein the crosslinking of the rubber was carried-out with hydrosilation crosslinking system and at low concentrations of the catalyst. The obtained thermoplastic elastomer compositions were of higher hardness and the thermoplastic olefinic resin was essential for the preparation of the composition.
U.S. Pat. No. 5,936,028 teaches an improvement in the process for hydrosilation crosslinking of a diene-containing elastomer in presence of a olefinic thermoplastic resin, wherein the oil was substantially free of sulfur. The obtained thermoplastic compositions were of high hardness and required the presence of a thermoplastic olefinic resin.
U.S. Pat. No. 6,069,202 teaches a thermoplastic elastomer composition that is prepared by blending a polar thermoplastic and non-elastomeric resin, olefinic rubber, and halogenated rubbery copolymer, wherein the rubbers are dynamically vulcanized. The thermoplastic compositions were of high hardness and the preparation required the presence of a polar and non elastomeric thermoplastic resin selected from polyamide, polycarbonate, polyester, polysulfone, polylactone, polyacetals, acrylonitrile-butadiene-styrene-resin, polyphenylene oxide, polyphenylene sulfide, styrene acrylonitrile and the like.
U.S. Pat. No. 6,084,031 teaches a thermoplastic elastomer composition prepared with a thermoplastic resin and a butyl rubber. The thermoplastic olefinic and crystalline resins were essential for the preparation of the compositions and as a consequence, compounds of high hardness were obtained.
U.S. Pat. No. 6,150,464 also teaches a thermoplastic vulcanizate that is prepared with a thermoplastic resin and a crosslinked rubber. The compositions require the crosslinking be carried-out in the presence of the crystalline resins, and again compositions of high hardness were obtained.
U.S. Pat. No. 6,147,160 teaches the preparation of a thermoplastic elastomer prepared with a thermoplastic resin and a butyl rubber. The compositions of high hardness were prepared.
U.S. Pat. No. 6,169,145 teaches a thermoplastic elastomer comprising a blend of a thermoplastic polyolefin resin and a rubber containing carbonyl functional groups. The compositions of high hardness were prepared.
U.S. Pat. No. 6,251,998 teaches a thermoplastic elastomer composition that is prepared with a thermoplastic resin and a ethylene-propylene-diene rubber with vinyl norbornene.
U.S. Pat. No. 6,437,030 teaches the preparation of a thermoplastic elastomer composition prepared with a thermoplastic crystalline resin and a rubber, wherein the dynamic vulcanization of the rubber was carried-out using a phenolic resin in the presence of a catalyst formed by a metal halide and a metal carboxylate.
There is a growing demand for a wide variety of articles that are soft and soothing to touch. It is, of course, also important for these articles to have the strength, durability, and rigidity needed in the applications where the articles are used. This can be accomplished by overmolding a soft thermoplastic composition onto on a hard thermoplastic substrate. However, there is a need for a soft thermoplastic elastomer composition that can be overmolded onto a hard thermoplastic resin substrate wherein the soft thermoplastic composition has lower hardness, good oil resistance and low compression set. There is currently a need for a thermoplastic elastomer composition that has superior feel and comfort as characterized by a lower modulus and lower hardness. There is a need for a soft thermoplastic elastomer composition that is very soft and has a unique, comfortable feel that is not otherwise attainable when a hard thermoplastic resin is present in the composition. There is a need for a thermoplastic elastomer (TPE) composition with a Shore A hardness as low as about 5 that is non-tacky, has good balance of oil resistance and compression set properties, low compressive modulus, unique feel, and can be made essentially odor-free which is obtained by dynamically crosslinking a diene containing elastomer and in the absence of a hard thermoplastic resin. Furthermore, there is a commercial need for soft and durable compositions with a Shore A hardness in the range of 5–30 that are obtained by dynamic crosslinking of styrene-butadiene random copolymer or ethylene-propylene-diene rubber.